An organic electroluminescent device (referred to as “organic EL device” hereinafter) has characteristics of low voltage, high brightness and large viewing angle, and it is expected that a display (organic EL display) having the above organic EL device will be developed to a broad range of uses.
Features of such an organic EL device include the feature that, in principle, hues of blue to red can be obtained as required.
Above all, a white organic EL device can be used directly as a white light source, so that it is expected to be used in the fields of thin film light source backlights for LCD, illumination lamp sources for use in a vehicle or an office, full-color displays such as TV, etc., and the like.
For establishing its use for illumination lamp sources or full-color displays, there is required a white organic EL device having high efficiency and high lifetime. In particular, when the use in displays is considered, there is further required a three-band white organic EL device that has an emission peak in each of wavelength regions of three primary colors of light in addition to the above performances.
As a white organic EL device, for example, there is disclosed an organic EL device having a blue emitting layer adjacent to a hole transporting layer and having, next thereto, a green emitting layer having a region containing a red fluorescent layer (see Patent Document 1).
Further, there is disclosed a white organic EL device that has three types of emitting layers having different carrier transport characteristics for emitting blue light, green light and red light (see non-Patent Document 1).
Further, there is also disclosed a white organic EL device containing emitting layers for emitting blue light in a broad range and red light in a broad range upon electron-hole recombination (see Patent Document 2).
Further, there is also disclosed a white organic EL device containing layers for emitting light in red, blue and green, which layers are isolated with hole-barrier layers (see non-Patent Document 2).
In these devices, however, it is required to control the concentration of a dopant contained in a trace amount, and it is difficult to control the same in a large-scale production process.
Further, there is disclosed a white organic EL device having an emitting layer comprised of three layers, a blue emitting layer, a green emitting layer and a red emitting layer which are stacked in this order from an anode, the blue emitting layer being constituted by incorporating a blue fluorescer into a blue emitting material, the green emitting layer being constituted by incorporating a green fluorescer into a blue or green emitting material, the red emitting layer being constituted by incorporating a red fluorescer into a blue emitting material (see Patent Document 3).
However, the efficiency of this device at a brightness of 200 cd/m2 is as insufficient as 3.7 to 3.9 lm/W.
Further, there is also disclosed a three-band white organic EL device in which a region on the side of a hole transporting layer adjacent to a blue emitting layer is doped with a yellow fluorescer and a region on the side of an electron transporting adjacent to the blue emitting layer is doped with a green fluorescer (see Patent Document 4).
However, the efficiency of this device is also as insufficient as 4-5 cd/A.
Further, there is also disclosed a technique of suppressing a change in hue of emitted light on the basis of a driving current in a device having an emitting layer comprised of a red emitting layer, a blue emitting layer and a green emitting layer which are stacked in this order from the anode side, the blue emitting layer as an intermediate layer being doped with an auxiliary dopant that exhibits red light fluorescence (see Patent Document 5).
While a change in hue of emitted light may be suppressed by this technique, nothing is disclosed with regard to the luminous efficiency of a white light device, so that the performance of the device is specifically unclear. Further, white light can be obtained only when the doping concentration of red fluorescer in the blue emitting layer is controlled to be a very small amount, and it is difficult to secure the reproducibility, etc., of making the device.
On the other hand, there is developed a white organic EL device using an unsymmetrical anthracene compound as a host material in an emitting layer (see Patent Document 6).
Further, there is developed an organic EL device using an aromatic amine derivative having an anthracene skeleton as a green dopant for forming a green emitting layer (see Patent Documents 7 and 8).
[Patent Document 1] JP-A-7-142169
[Patent Document 2] U.S. Pat. No. 5,405,709
[Patent Document 3] JP-A-10-3990
[Patent Document 4] JP-A-2003-86380
[Patent Document 5] JP-A-2004-6165
[Patent Document 6] Japanese Patent Application No. 2004-042694
[Patent Document 7] Japanese Patent Application No. 2003-106231
[Patent Document 8] Japanese Patent Application No. 2003-76772
[Non-Patent Document 1] “Science” 1995, Vol. 267, page 1332
[Non-Patent Document 2] “Applied Physics Letters”, 1999, Vol. 75, page 888
It is an object of the invention to provide a three-band white organic EL device having high brightness, high efficiency and high lifetime and having excellent coloring rendering properties.
The invention provides the following white organic EL device.    1. A white organic electroluminescent device comprising an emitting layer interposed between an anode and a cathode,
the emitting layer emitting blue light, green light and red light,
the emitting layer containing a green dopant that is an aromatic amine compound represented by formula (1),
wherein A1 to A2 are independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 nucleus carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted aryamino group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted alkylamino group having 1 to 10 carbon atoms or a halogen atom; d and e are independently an integer of 1 to 5; h is an integer of 1 to 9; when d and e are independently 2 or more, A1s and A2s may be the same or different and may be joined together to form a saturated or unsaturated ring; provided that compounds where both of A1 and A2 are hydrogen atoms are excluded;
R11 is a substituted or unsubstituted secondary or tertiary alkyl group having 3 to 10 carbon atoms or a substituted or unsubstituted secondary or tertiary cycloalkyl group having 3 to 10 carbon atoms; f is an integer of 1 to 9; when f is 2 or more, R11s may be the same or different; R12 is a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 nucleus carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted arylamino group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted alkylamino group having 1 to 10 carbon atoms, or a halogen atom; g is an integer of 0 to 8; when g is 2 or more, R12s may be the same or different; and
f+g+h is an integer of 2 to 10.    2. The white organic electroluminescent device according to 1, wherein the emitting layer has a three-layer structure of a blue emitting layer emitting blue light, a green emitting layer emitting green light and a red emitting layer emitting red light.    3. The white organic electroluminescent device according to 1, wherein the emitting layer has a two-layer structure of a blue emitting layer emitting blue light, and a green/red emitting layer emitting green light and red light.    4. The white organic electroluminescent device according to any one of 1 to 3, wherein the emitting layer contains a host material that is an unsymmetric anthracene compound.    5. The white organic electroluminescent device according to 4, wherein the unsymmetric anthracene compound is a compound represented by formula (2).
wherein Ar1 and Ar2 are independently a substituted or unsubstituted aryl group having 6 to 50 nucleus carbon atoms, provided that Ar1 and Ar2 do not have the same structure,
R1 to R8 are independently a hydrogen atom, a substituted or unsubstituted aryl group having 6 to 50 nucleus carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted alkyl group having 1 to 50 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 50 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 50 carbon atoms, a substituted or unsubstituted aryloxy group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted arylthio group having 5 to 50 nucleus carbon atoms, a substituted or unsubstituted alkoxycarbonyl group having 2 to 50 carbon atoms, a substituted or unsubstituted silyl group having 1 to 50 carbon atoms, a carboxyl group, a halogen atom, a cyano group, a nitro group or a hydroxyl group.    6. A white organic electroluminescent device comprising an anode, an emitting layer and a cathode,
the ionization potential of a green dopant forming the emitting layer being equal to or larger than the ionization potential of a blue dopant forming the emitting layer.    7. A white organic electroluminescent device comprising in sequence an anode, a blue emitting layer, a green emitting layer, a red emitting layer and a cathode,
the ionization potential of a green dopant forming the green emitting layer being equal to or larger than the ionization potential of a blue dopant forming the blue emitting layer.    8. A white organic electroluminescent device comprising in sequence an anode, a blue emitting layer, a red emitting layer, a green emitting layer and a cathode,
the ionization potential of a green dopant forming the green emitting layer being equal to or larger than the ionization potential of a blue dopant forming the blue emitting layer.    9. The white organic electroluminescent device according to any one of 2 to 5, 7 and 8, wherein a blue dopant forming the blue emitting layer is at least one compound selected from styryl amines, amine-substituted styryl compounds, amine-substituted condensed aromatic rings and condensed-aromatic-ring containing compounds.    10. The white organic electroluminescent device according to any one of 2 to 5, 7, 8 and 9, wherein a red dopant forming the red emitting layer is a compound containing a fluoranthene skeleton or perylene skeleton.
According to the invention, there can be provided a three-band white organic EL device having high brightness, high efficiency and high lifetime and having excellent color rendering properties.